Abstract
A clastic-dominated sedimentary succession is exposed in different localities at the central part of western Saudi Arabia, unconformably overlying the weathered Precambrian Arabian Shield rocks. The age and chronological relationships of the different formational names applied to that succession is still a matter of debate among geologists. The succession is assigned to Cretaceous-Eocene or Oligo-Miocene according to the ages of the overlying Tertiary basic volcanics (harrat).
Highlights
A sedimentary succession dominated by clastics rests nonconformably on the basement rocks of the Arabian Shield at the west central part of Saudi Arabia
The main concern of the present study is to propose a new age for Usfan and Haddat Ash Sham formations and correlate them biostratigraphically
Fossils were collected from the carbonate and marly layers, they are dominated by bivalves with fewer gastropods and cephalopods
Summary
A sedimentary succession dominated by clastics rests nonconformably on the basement rocks of the Arabian Shield at the west central part of Saudi Arabia. The succession known as the Shumaysi Formation is rich in economic iron ores [3,4] It yielded few marine but many freshwater molluscan [5] and is assigned a younger age (early Eocene) than Usfan and Haddat Ash Sham formations (Cretaceous - Eocene or Oligo-Miocene). The succession known as the Umm Himar Formation is lithologically and paleontologically different It rich in vertebrate fossils (shark teeth, catfish, lung fish, turtles and crocodiles), it was deposited in an estuarine environment and is assigned a Paleocene age [7]. The area comprises the following main rock units (I) Older Pre-Cambrian igneous and metamorphic rocks of the Arabian shield; (II) sedimentary succession comprising the economic iron ores and clays deposits and the carbonate beds (the aim of the present study); (III) Tertiary basic volcanics (Harrat); (IV) Quaternary deposits (Figure 1)
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